Induction speed governor



April 12, 1966 J. HELFNER ET AL 3,246,224

INDUCTION SPEED GOVERNOR Original Filed Dec. 20, 1960 I NVENTOR5 Jl/LES HELFNER United States Patent 3,246,224 INDUCTION SPEED GOVERNOR Jules Helfner, Massapequa, and Paul Fenster, Brooklyn, N.Y., assignors to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Original application Dec. 20, 1960, Ser. No. 77,089, now Patent No. 3,129,370, dated Apr. 14, 1964. Divided and this application Sept. 12, 1963, Ser. No. 315,732

2 Claims. (Cl. 318-629) This application is a division of our copending application Serial No. 77,089, now Patent No. 3,129,370 filed December 20, 1960.

Our invention relates to an induction speed governor and more particularly to an improved speed governor which is more reliable and which is more easily adjusted than are speed governors of the prior art.

There are known in the prior art governors for regulating the speed of electric motors. One type of governor consists essentially of a centrifugal switch connected in the motor supply line which opens and inserts a resistance in the line when certain speeds are attained. The speed at which the switch opens is determined by the governor setting. While the governor is operating, the current to the motor is continuously established and is partially interrupted by the centrifugal switch. Governors of the type described above embody a number of disadvantages. First, since they embody vibrating contacts, problems of arcing and contact point burn out exist. Thus the life of the governor is limited by the life of the contact points. Secondly, the unit is not as reliable as is desired, since the contacts become dirty and, in an extreme case, they may fuse. A further disadvantage of governors of this type is that the motor must be stopped to permit the setting of the governor to be changed. Moreover, a change in the setting affects the dynamic balance of the rotor.

We have invented an induction speed governor which overcomes the disadvantages of governors of the prior art pointed out hereinabove. The setting of our governor may be changed without stopping the motor and without affecting the dynamic balance of the rotor. Our improved governor has no vibrating contacts so that problems of arcing and contact point burn out are eliminated. Thus, our governor is more reliable than are governors of the prior art.

One object of our invention is to provide an induction speed governor the setting of which may be changed without stopping the motor which it controls.

A further object of our invention is to provide an induction speed governor which has no vibrating contacts.

A still further object of our invention is to provide an induction speed governor which is more reliable than are governors of the prior art.

Other and further objects of our invention will appear from the following description.

In general, our invention contemplates the provision of an induction speed governor in which a magnet driven by the motor to be controlled vibrates a reed at a frequency somewhat less than the natural frequency of vibration of the reed. In response to reed vibration, there is produced an electrical effect which increases with the amplitude of vibration to control motor speed. In one form of our invention we feed a voltage generated in response to vibration in the reed to the armature of a direct current motor to oppose the armature voltage. In another form of our invention in response to changes in reed vibration the inductance of an inductor in the circuit of an alternating current motor varies.

In the accompanying drawings which form part of the necessary specification and which are to be read in conice junction therewith and in which like reference characters are use to indicate like parts in the various views:

FIGURE 1 is a schematic view of one form of our induction speed governor used to control the speed of a direct current motor.

FIGURE 2 is a schematic view of another form of our induction speed governor used to control the speed of an alternating current motor.

FIGURE 3 is a curve illustrating the response of the reed of our induction speed governor.

Referring now to FIGURE 1 of the drawings, a direct current motor indicated generally by the reference character 10 has an armature 12 adapted to be supplied with energy by brushes 14 and 16 in engagement with a commutator 18. The field for the motor 10 may be provided by a permanent magnet having a north pole 22 and a south pole 24. When armature 12 is energized, shaft 26 rotates in a manner known to the art.

We mount a permanent magnet 28 on shaft 26 for rotation therewith. Magnet 28 is an elongated bar magnet having a north pole at one end thereof and a south pole at the other end. We mount a reed 30 formed from a suitable resilient material in a supporting bracket 32 in which the reed 30 is secured by a screw 34. Bracket 32 may be adjustably positioned on a suitable stationary support 36 by means of a set screw 38 or the like.

We secure a small permanent magnet 40 to the reed 30 for movement therewith. As the bar magnet 28 rotates it alternately attracts and repels the magnet 40 thus to impart a vibration to the reed 30. It will be appreciated from the description of the second form of our invention given hereinafter that we could alternately make the reed 30 of a magnetic material in which case the rotation of the permanent magnet 28 would cause the reed to vibrate. We dispose the magnet 40 in a position at which upon vibration of reed 30 it moves into and out of a winding 42 to induce a voltage in the winding. We connect a rectifier 44 and a resistor 46 in series across the coil 42 so that a direct current potential of the polarity indicated exists across resistor 42. We connect the terminals of the resistor 46 respectively to brush 14 and to the positive terminal 48 of a source of direct current potential the negative terminal of which is connected to brush 16.

Referring now to FIGURE 3, we have shown the response curve of the reed 30 as a plot of the amplitude of the vibration as a function of the frequency to which the reed vibrates. As can be seen by reference to the curve, when the reed is driven at its natural frequency, then the amplitude of the vibration is extremely large. We so construct and support the reed 30 as to have a natural frequency of vibration which is somewhat greater than the frequency at which the motor drives the reed when the motor is operating at its desired speed. Thus if the motor tends to speed up, the amplitude of vibration of the reed 30 will increase as well as its frequency of vibration with the result that magnet 40 enters further into coil 42 and the voltage of register 46 increases. It will be seen that this voltage opposes the motor armature voltage so that as the voltage on resistor 46 increases then the motor slows down.

Referring now to FIGURE 2, we have illustrated another form of our invention in which reed 30 is fixed in a stationary support 52. The motor to be controlled in this case may be an alternating current servomotor 54 adapted when energized to drive its shaft 56 carrying the magnet 38. In this form of our invention we mount a slug 58 of magnetic material on the reed 30 so that when magnet 28 rotates it vibrates the reed 30. We could, of course, form the reed 30 itself of magnetic material. We connect a pair of induction coils 60 and 62 in series with motor 54 across a source 64 of alternating current. The end of the reed 30 remote from the support 52 carries for movement therewith a pair of slugs 66 and 68 of magnetic material. When, as magnet 28'rotates, reed 30 vibrates slugs 66 and 68 alternately move into and out of the respective windings 60 and 62 thus to vary the inductance in circuit. We so construct the assembly of the reed 30 and the slugs 66 and 68 as to have a natural frequency of vibration somewhat greater than the frequency of vibration when motor 54 is operating at the desired speed. Thus as the motor speed increases the amplitude of motion of the reed 30 increases and a greater change in inductance in the circuit is produced. Consequently, the current in the motor 54 drops and its speed decreases. It will be understood of course that the reed 30 in the form of our invention shown in FIGURE 2 may be adjusted in length. A screw 59 may be actuated to vary the center of gravity of the reed.

In operation of the form of our invention shown in FIGURE 1 when motor is energized it drives shaft 26 to rotate magnet 28 to cause reed 30 to vibrate. When the motor is operating at the desired speed, the potential across resistor 46 causes the armature potential to be that potential required to keep the motor rotating at its desired speed. If for any reason the motor speeds up the amplitude of motion of reed 30 changes to increase the potential across resistor 46 to decrease the armature potential'to cause the motor to slow down. Consequently, if the motor speed drops below the desired speed, the potential across resistor 46 drops and the motor speeds up.

The setting of the governor may readily be changed by changing the effective length of reed 30. This can be accomplished bymoving bracket 32 along the length of the reed and by repositioning the bracket properly to locate magnet 40.

In operation of the form of our invention shown in FIGURE 2 when motor 54 is energized, shaft 56 rotates to cause magnet 28'to vibrate reed 30. As the reed vibrates, slugs 66 and 68 move into and out of windings 6i) and 62 to present a certain effective inductance to the circuit. If the motor is rotating at a great speed, than the inductance is such as will keep the'motor rotating at this speed. As, however, the speed of the motor changes, the effective inductance changes in a direction to cause the motor to return to the desired speed.

It will be seen that we have accomplished the objects of our invention. Wehave provided an induction speed It is furtherobvious that various changes may be made in details within the scope of our claims without departing from the spirit of our invention. It is, therefore, to be understood that our invention is not to be limited to the specific details shown and described.

Having thus described our invention, what we claim 1. An induction speed governor for a motor having a shaft including in combination an element having a natural frequency of vibration, means responsive to rotation of said shaft for vibrating said element at a frequency in the region of said natural frequency, a source of alternating voltage, a variable impedance, means connecting said source and said impedance and said motor in series and means responsive to vibration of said member for varying said impedance.

2. An induction speed governor for a motor having a shaft and'having an input circuit for applying a voltage to said motor including in combination a vibratory element, means mounting said element for vibratory movement at its natural frequency of vibration, means responsive to rotation of said shaft for vibrating said element at a frequency below said natural frequency of vibration, an inductance coil connected in said input circuit, a slug of magnetic material and means responsive to vibration of said element for moving said slug in inductively coupled relationship relative to said coil to vary the inductance of said coil.

References Cited by the Examiner UNITED STATES PATENTS 7/1961 Devol 318-329 ORIS L. RADER, Primary Examiner.

S. GORDON, Assistant Examiner. 

1. AN INDUCTION SPEED GOVERNOR FOR A MOTOR HAVING A SHAFT INCLUDING IN COMBINATION AN ELEMENT HAVING A NATRUAL FREQUENCY OF VIBRATION, MEANS RESPONSIVE TO ROTATION OF SAID SHAFT FOR VIBRATING SAID ELEMENT AT A FREQUENCY IN THE REGION OF SAID NATURAL FREQUENCY, A SOURCE OF ALTERNATING VOLTAGE, A VARIABLE IMPEDANCE, MEANS CONNECTING 